Injection molding machine for processing plastics

ABSTRACT

In an injection molding machine the injection molding unit and the mold closing unit are at least are at least partially operated by electrical drives in form of a linear motor. The rotor and the stator have cylindrical surfaces which are arranged concentrically. The stator windings are symmetrical to the motion axis of the linear motor. Several equally acting first cylindrical surfaces are interleaved with a corresponding number of equally acting other cylindrical surfaces and are respectively operated together for operative connection. This results in a linear motor that is able to provide the advance forces required for injection molding.

FIELD OF THE INVENTION

The invention relates to an injection molding machine and, moreparticularly, to an injection molding machine for processing plasticsmaterials and other plasticisable compounds including at least partiallyelectrically operated driving units to operate the machine.

DESCRIPTION OF THE RELATED ART

A linear motor, which is used as the driving unit and is provided with arotor and stator, is known for plastics material molding machines fromDE-T2 37 82 817, which corresponds to EP 0 280 743 B1, and JP-A 63-1516,rotor and stator having cylindrical surfaces which are in operativeconnection with one another. These surfaces permit the magnetic face,which is needed for the required advancing forces, to be suitablyincorporated in the drive axis. If stator windings are symmetricallydisposed in accordance with DE-A 44 45 283, the relatively high bearingforces caused by the magnetism are mutually excluded. However, eventhere, mention is constantly made in the description of only one primarypart and one secondary part, which parts co-operate accordingly with oneanother. If FIG. 3 there is additionally considered, it becomes apparentthat the internally situated pipe is merely a carrier pipe which, justlike the externally situated pipe, is neither a stator nor a rotor. Whensuch a linear motor is used, there is a simultaneous saving in thecomplex converting means, which are susceptible to wear and serve toconvert a rotary movement into a linear movement, such as, for example,a transmission mechanism, a spindle, levers and toothed rods (cf alsoEP-A 744 815), but the forces, which are required for a plasticsmaterial injection molding machine, cannot yet be applied,therefore to asufficient extent.

Electrical driving units are also often used in conjunction withinjection molding machines. thus, for example, it is known from EP 0 662382 to stack together various hollow-shaft motors inside the injectionmolding unit to inject the plasticised compound into the injection mouldand to fit the nozzle onto the injection mould. However, it is necessaryfor such purpose, and time-consuming, to convert the rotary movements,produced by the hollow-shaft motors, into translatory movements.However, since all of the shafts or axis for the injection moldingmachine are translatory shafts with the exception of the feed screw formetering the material to be plasticised, the use of such hollow-shaftmotors is only recommended to a limited extent.

From handling techniques and medical techniques, linear motors are knownwhich, however, do not have sufficient advancing forces, so that thelinear motors, which are mainly fitted in a flat manner, are notsuitable for use in an injection molding machine. (Company brochureentitled “New linear Motors and its applications” produced by thecompany called Fanuc, published in FANUC Tech. Rev. 112, pp. 25-36(December, 1998); specification sheet linear motors entitled Lin.Mot Pbelonging to Sulzer Electronics AG, Zurich.)

SUMMARY OF THE INVENTION

The present invention provides a linear motor for an injection moldingmachine, which motor can also apply the advancing forces required for aninjection molding machine.

An injection molding machine for processing plastics materials andplasticisable materials of the present invention includes an injectionmolding unit and a mould closing unit, which are operated at leastpartially by an electric driving unit including at least one linearmotor, which has a rotor with magnets, disposed along a firstcylindrical surface, and a stator with stator windings disposed along asecond cylindrical surface, the first and second cylindrical surfaces ofstator and rotor being concentrically disposed, and the stator windingsbeing substantially symmetrical relative to an axis of movement of thelinear motor. Additionally, a plurality of identically acting firstsurfaces are stacked with a corresponding number of identically actingsecond surfaces, the first and/or second surfaces each being operablejointly in operative connection.

In consequence, various cylindrical faces can be stacked one inside theother so that a plurality of identically acting magnetic faces areproduced which contribute towards increasing the advancing forces up toa range which is required for plastics material injection moldingmachines, e.g. for applying the closing force. The alleged disadvantageis tolerated in such case, i.e. that the linear motor can tilt moreeasily so that greater demands for precision are to be made on the meansfor guiding the parts of the linear motor. However, this is compensatedfor again by the more compact construction which can be achieved.

Although it is known, in prior art, which forces are required for aninjection molding machine to produce molded parts, only circulararrangements were proposed there, the rotor and stator having concentricsurfaces, since the person skilled in the art has probably concludedtherefrom, incorrectly, that a corresponding alternative arrangementcannot be achieved to a suitable extent. In order to operate thesurfaces jointly in operative connection with one another in fact, saidsurfaces have to be worked with appropriate precision. In such case, theprecision required for the operation of the linear motor increasesexponentially with an increasing spacing from the central line of thecylindrical surfaces so that the linear motor can tilt more easily, thegreater this spacing is, more especially when the linear motor is to bekept short in order to achieve as compact a construction of the entireinjection molding machine as possible. This is further emphasized by thehigh temperatures which occur at high forces. This may probably also bethe reason why, despite their advantages, linear motors have not yetbeen successful in the field of plastics material injection moldingmachines, since hitherto the corresponding forces could still not beapplied.

Cooling ducts may be disposed in the cylindrical walls of the stator, sothat the heating, caused by the current, can be reliably dissipated. Thecooling medium used therefor can, at the same time, be used to controlthe temperature of other component parts in the injection moldingmachine.

BRIEF DESCRIPTION OF THE FIGURES

The invention is explained hereinafter with reference to a plurality ofembodiments which are illustrated in the accompanying Figures. In thedrawing:

FIG. 1 illustrates an injection molding unit moved onto the stationarymould carrier of a mould closing unit;

FIG. 2 is a horizontal sectional view through the injection molding unitin the region of carrier block and injection bridge;

FIG. 2a is a sectional view taken along the line 2 a—2 a of FIG. 2;

FIG. 3 is a sectional view according to FIG. 2 of an alternativeembodiment;

FIG. 4 illustrates an enlarged portion taken from FIG. 3 in the regionof the injection bridge;

FIG. 5 is a side elevational view of a mould closing unit, which isshown partially in section;

FIG. 6 illustrates an enlarged portion taken from FIG. 5 in the regionof the movable mould carrier;

FIG. 7 is a side elevational view, shown partially in section, of a5-point toggle lever of a mould closing unit;

FIG. 8 is an enlarged view of one of the two 5-point toggle leversaccording to FIG. 7;

FIG. 9 illustrates a mould closing unit having a Y-shaped toggle lever;

FIG. 10. illustrates the enlarged Y-shaped toggle lever;

FIG. 11 is a horizontal sectional view through an injection molding unitin the region of the carrier block and injection bridge in analternative embodiment;

FIG. 12 is a side elevational view, shown partially in section, of amould closing unit of the pulling type;

FIGS. 13 and 14 are views according to FIG. 11 of injection moldingunits in two additional embodiments; and

FIG. 15 illustrates an injection molding unit provided with a closurenozzle.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The invention is now explained more fully, by way of example, withreference to the accompanying drawings. However, the embodiments areonly examples which are not to restrict the inventive concept to onespecific arrangement.

FIG. 1 illustrates initially the injection molding unit of an injectionmolding machine for processing plastics materials and otherplasticisable compounds, such as, for example, ceramic or metallicpulverulent compounds. A plasticising cylinder P is accommodated in theinjection molding unit on a carrier block 52. The plasticisable compoundis plasticised in the plasticising cylinder and injected into aninjection mould M via a nozzle 21. For such purpose, the nozzle 21penetrates the stationary mould carrier 14. The front portion of theinjection molding unit S is supported on the machine base 51 via asupporting member 22 and guided and supported on the machine base via aguiding element 53. In order to fit the nozzle 21 onto the injectionmould M, and to remove such if necessary, nozzle driving units 50 areprovided which are hydraulically configured in FIG. 2. The cylinders ofthe hydraulic nozzle driving unit 50 form, with the carrier block 52 anda closure 54, a rigid frame which is guided on guide bars 20. Theguiding element 53 is guided on the cylinders of the nozzle drive 50.

In order to inject plasticised material into the injection mould, aninjection unit E is provided. When the injection unit is actuated, theinjection bridge 23 and, hence, the feed screw is axially moved. Theinjection bridge 23 carries the metering motor 28, by means of which afeeding means15—a feed screw in the embodiment—can be rotated. While themetering motor 28 has to produce a rotary movement to rotate the feedingmeans15, translatory movements are required to drive the nozzle and forinjection purposes. A linear motor is used as the electrical drivingunits for these translatory movements, and it includes a rotor havingmagnets disposed along a first cylindrical surface 11. The linear motoralso has a stator with stator windings 26 disposed along an additionalcylindrical surface 12. The cylindrical surfaces 11 and of the statorand rotor are concentrically disposed, so that the magnetic face, whichis required to produce suitable advancing forces for movements in theinjection molding machine, can be increased. So that the relatively highbearing forces are eliminated, not only are the circular surfacesprovided; additionally the stator windings 26 and preferably also themagnets 25 of the stator are disposed symmetrically relative to the axisof movement a—a of the linear motor. FIG. 2a illustrates the circularsurfaces and shows the application of corresponding forces on the basisof the force density which can be achieved at these faces.

In all of the embodiments, what is to be understood by the term surfacesis both the external surface of a cylinder and the internal surface of apipe; in both cases, cylindrical surfaces 11 and 12 are involved. Themagnets 25 may be permanent magnets, but they may also be separatelyexcited coils having an iron core. Furthermore, the driving unit may beoperated in a controlled or regulated manner, that is to say, forexample, it can be operated as a servomotor over a regulating path.

In the case of the injection molding units illustrated in FIGS. 1 and 4,the linear motors of the injection unit are so disposed that the axis ofmovement a—a of the linear motor is, at the same time, the injectionaxis s—s of the injection molding unit S. When transferred to the mouldclosing unit shown in FIGS. 5-8 (see below), the axis of movement a—a ofthe linear motor is, at the same time, the axis of symmetry s—s of themould closing unit F. For simplification purposes, the sameidentification s—s is used in both cases, and also, moreover, thereference numerals in the drawings are so selected that identicallyacting parts are provided with identical reference numerals.

To produce the necessary advancing forces, the cylindrical faces aredisposed in a stacked manner. FIGS. 2 and 2a illustrate how a pluralityof identically acting first surfaces 11 are stacked with a correspondingnumber of additional surfaces 12 for the injection movement. A cylinder60 is supported on the closure 54, which is moved jointly with thecarrier block 52 via the nozzle driving unit 50 as a consequence of theconnection, and it has identically acting surfaces on its inside and onits outside. It may be open to question whether these surfaces areinitial surfaces of the rotor or additional surfaces of the stator. Inthe embodiment, the surfaces of the cylinder 60 are first surfaces ofthe rotor. These surfaces are formed by identically acting additional orfirst surfaces of two concentric cylinders 70 and 71. When viewedexternally, the impression is given that piston rod and cylinder of apiston-cylinder-unit would extend into one another. The surfaces are sodisposed that the internal surface of the external cylinder 70co-operates with the outside of the cylinder 60, and the externalsurface of the internal cylinder 71 co-operates with the inside of thecylinder 60. A greater advancing force than was usual hitherto can beproduced by this stacking arrangement.

In order to protect the linear motor from contamination and, ifnecessary, to produce a chamber which can be provided with a suitablelubricant, an additional cylinder 17 moves jointly with the cylinder 60and is, in this respect, just like the cylinder 60 connected to theclosure 54. This cylinder 17 overlaps the linear motor and has, at itsfront end on the left of FIG. 2, a mounting 18 which cooperates with abearing face 19 of the cylinder 70. The parts of the linear motors areguided towards one another via mounting 18 and bearing face 19, and, inconsequence, the parts of the injection molding machine are centered inorder to ensure a precision which is required to produce high-qualityparts. At the same time, the mounting 18 and bearing face 19 act in asealing manner.

If the stator windings of the concentric cylinders 70 and 71 areenergized, an advancing movement results in co-ordination with themagnet of the cylinder 60. While the cylinder 60 remains in an unchangedmanner, the concentric cylinders 70 and 71 are moved jointly with theinjection bridge 23. FIG. 3 illustrates an alternative embodiment of theinjection molding unit S, where cylinder 60 and concentric cylinders 70and 71 have been reversed. The cylinder 60, with which the cylinders 70and 71 co-operate, is mounted on the carrier block 52, said cylindersnow being a component part of the injection bridge 23. The reversalnecessitates a reversal of rotor and stator. If, in the firstembodiment, the cylinder 60 was the rotor, then it is now the stator.The injection bridge 23 also slides here on the cylinders of thehydraulic nozzle driving unit, but a frame, which reinforces theinjection molding unit S per se, is not provided as in the first case.The additional cylinder 17 supports the linear motor by means ofmounting 18 and in co-operation with the bearing face 19.

According to FIG. 3, the stator windings 26 can be divided into aplurality of separate electrical switching zones along their axis ofmovement a—a. The entire range of movement is shown by the range D.During displacement, all of the switching zones A, B and C are involvedduring the injection operation, above all towards the end, in order topermit the required forces to be applied with the participation of allof the switching zones. However, as soon as a specific zone is no longerin operative connection with the surfaces of the rotor by means of itsface, the zones which are no longer required can be switched-off to saveenergy.

Cooling ducts 27, which lie behind or adjacent the stator windings 26when viewed from the magnets 25, are associated with said statorwindings in the cylindrical walls of the stator, so that the heating,caused by the current, can be reliably dissipated. The cooling mediumemployed may be used at the same time to control the temperature ofother component parts in the injection molding machine.

The enlarged portion according to FIG. 4 shows that the magnets 25 arealso attached to the walls of the cylinders 70 and 71. The magnets areprovided with the identifications for their north-south (N-S) poles. Thestator windings 26, however, are identified with U-V. The injectionbridge, which is substantially formed by the concentric cylinders 70 and71, has sufficient space in its center, that is to say in the center ofthe cylinder 71, to support the metering motor 28 as well as the lockingarrangement for the feeding means15.

The linear motor, as an electrical driving unit, may also be employedfor other assemblies of the injection molding machine. It is possible,more especially, to provide the translatory shafts with linear motors.On the injection molding side, such shafts are the driving unit forfitting the nozzle 21 onto the injection mould as well as the alreadyexplained injection means E or the actuating mechanism for a closurenozzle V (FIG. 15). On the side of the mould closing unit F, this is,for example, the closure mechanism for moving the movable mould carrier13 towards and away from the stationary mould carrier 14, which mayapply the closing force if necessary. If the mould closing unit isconstructed so that the closing mechanism only accomplishes the mouldclosing movement, while the closing force is applied by a separatearrangement, this separate arrangement may be provided with a linearmotor. On the mould closing side, an ejector unit 16 or a core pullerunit K (FIG. 5) on the injection mould M may also be provided with alinear motor.

FIG. 5 illustrates a mould closing unit F, wherein the movable mouldcarrier 13 is moved along guide bars 56 by means of the closingmechanism. During displacement, the injection mould M is alternatelyclosed and opened. The closing mechanism is supported on a supportingelement 57. FIG. 6 illustrates an enlarged portion of FIG. 5 in theregion of the movable mould carrier. A comparable construction, such aswas previously the case with the injection molding unit, is alsoapparent here. A cylinder 60, with an inside and an outside, is therotor with the magnet 25. The movable mould carrier, however, carriesthe concentric cylinders 70 and 71 as the stator. The cylinder 60 andthe additional cylinder 17 are mounted on the supporting element 57,said additional cylinder being mounted and guided on the bearing face 19here also with the mounting 18. In the embodiment, therefore, relativelylarge cylinders are also stacked inside one another here. Sufficientspace is available in the interior of the cylinder 71 to accommodate anejector unit 16, which is also actuated as a linear motor. An extremelyshort structural design is therefore produced.

If desirable, however, a plurality of individual cylinders may also bestacked around the closing axis s—s and/or disposed concentrically,which cylinders are then operated identically in this respect.

The linear motor may also be used for other types of closing mechanisms,though the description of the stacking has been somewhat curtailedhereinafter to achieve a clear description. FIGS. 7 and 8 illustrate aclosing mechanism with a multi-point toggle lever, here a 5-point togglelever. The movable mould carrier is guided on guide bars 56, and anejector unit is to be actuated centrally in the movable mould carriervia a linear motor. FIG. 8 illustrates the structure of the 5-pointtoggle lever 80. The toggle lever is supported on the supporting element57 by the pivot joint 84. It is supported on the movable mould carrier13 by the pivot joint 86. The pivot joints 84 and 86 are interconnectedvia two arms 87 and 88 which, in turn, for their part are pivotallyinterconnected at the pivot point 85. A pivot point 83 for a pivotal arm81 is provided on the arm 87. Said pivotal arm communicates with thedrive at the pivotal point 82. If the drive is moved linearly along theclosing axis, the arm 81 urges the arm 87 in an arc forwardly and thenupwardly. The arms 87 and 88 thereby come into an extended position andare prevented from falling-back by automatic locking, supported by thearm 81. The advantage of this embodiment is that, in the extendedposition, no force has to be applied to the arm 81 in order to maintainthe extended position. This is advantageous since, during the linearmovement, the covering of the cylindrical surfaces 11 and 12 alsoreduces, so that the force, produced by the linear motor, is smallertowards the end of the movement. FIG. 8 also shows that the linear motorfor the ejector unit 16 can be guided back into the cylinder of thelinear motor of the closing mechanism 0.

An alternative type of closing mechanism is the Y-shaped toggle levershown in FIGS. 9 and 10, which is otherwise constructed like thepreviously described mould closing units F. The Y-shaped toggle lever 90supports the driving unit, in that it suspends said unit in a freelydisplaceable manner via two pivotal arms 91. If the rotor 30 is moved,it acts on the pivotal point 93 and brings the arms 92 into the extendedposition. Here also, a relatively small force is to be applied in theextended position. The rotor 30 may be so configured that, during theapplication of a small force, it only slightly co-operates with thesurfaces of the stator while, during the application of a high force, atotal co-operation of the surfaces 11 and 12 is effected.

It is thereby indicated that, basically, the cylindrical surfaces can beso disposed that, when a high force has to be applied, a large coveringof the surfaces 11 and 12 also exists, so that a high force is producedalso as a consequence of a large abutment face. This is explained for aninjection molding unit S with reference to FIG. 11. The linear motor isemployed as injection means E, wherein the covering of the cylindricalsurfaces 11 and 12 is increasing when the nozzle is fitted onto theinjection mould M. This is achieved when the cylinder 60 is supported onthe carrier block. Here, the cylinder 60 is the stator. In order to movethe injection bridge, the cylinders 70 and 71 are pulled over thecylinder 60 so that, during the injection process, a greater force isproduced the further the feed screw is moved in the direction towardsthe injection mould. In consequence, the injection bridge 23 moves tothe left in FIG. 11.

The same principle can also be achieved with the mould closing unit.FIG. 12 illustrates a linear motor as the closing mechanism, thecovering of the cylindrical surfaces 11 and 12 increasing during theapplication of the closing force. A mould closing unit is involved,wherein the movable mould carrier is pulled over the stationary mouldcarrier 14. In the embodiment, the bars 56 are not securedly mounted onthe stationary mould carrier. They are provided with the first surfacesin this region. If the stator is actuated on the stationary mouldcarrier, the rotor is pulled into the linear motor, so that a greatercovering of the surfaces is produced with an increasing closing movementof the injection mould M, and maximum force is achieved at the end ofthe mould closing movement. FIG. 12 also shows that the linear motor hasits axis of movement a—a coinciding with the central axis of the bar 56.

With an otherwise identical structure as in FIG. 3, FIG. 13 shows thatthe nozzle driving unit, which was hydraulic in FIG. 3, may also be inthe form of a linear motor. In this respect, the bars 20 are providedwith magnets, so that they may serve as rotors of the nozzle drivingunit N. They co-operate with a stator which slides along the bars 20.Because of this structure, a corresponding movement along the bars 20 ispossible.

In an alternative embodiment, FIG. 14 shows that the axis of movementa—a of the linear motor may also coincide with the central axis of theguide bars 20 in the injection molding unit. In this embodiment, astacking of injection means and nozzle driving unit N around the bars 20is created. The nozzle driving unit N lies around the bar 20. The guidebar is the rotor, while a sleeve represents the stator 40. This sleeveis the stator on the inside and, in turn, is already the rotor withmagnets for the injection means E on the outside. In consequence, anadditional sleeve is placed around the sleeve as stator 41, whichadditional sleeve is, for its part, also the injection bridge 23.Finally, the injection bridge carries the metering motor 28.

It is self-evident that this description may be subjected to the mostvaried modifications, changes and adaptations, which range fromequivalents to the dependent claims.

What is claimed is:
 1. Injection molding machine for processing plasticsmaterial and plasticisable materials, comprising: an electric drivingunit that is adapted to operate at least partially at least one of aninjection molding unit and a mould closing unit, the electric drivingunit including at least one linear motor, which has a rotor withmagnets, disposed along it first cylindrical surface, and a stator withstator windings disposed along a second cylindrical surface, the firstand second cylindrical surfaces being concentrically disposed, and thestator windings being substantially symmetrical relative to an axis ofmovement of the linear motor, wherein a plurality or identically actingfirst surfaces are stacked with a corresponding number of identicallyacting second surfaces, at least one of the first and second surfacesbeing operable jointly in operative connection, wherein the identicallyacting first or second surfaces are on an outside and inside of a firstcylinder, and wherein the identically acting first and second surfacesare so disposed on concentric second and third cylinders that aninternal surface of the second cylinder cooperates with the outside ofthe first cylinder, and an external surface of the third cylindercooperates with the inside of the first cylinder.
 2. Injection moldingmachine according to claim 1, wherein the magnets are separately excitedcoils with an iron core.
 3. Injection Molding machine according to claim1, wherein the electric driving unit is a regulated servo driving unit.4. Injection molding machine according to claim 1, wherein the linearmotor is cylindrical and is overlapped on the outside by a cylinder,which guides faces of the rotor and the stator, which are moved towardsone another, along a separate bearing face by means of at least onemounting.
 5. Injection molding machine according to claim 1, wherein thestator windings are divided along the axis of movement into a pluralityof separate electrical switching zones.
 6. Injection molding machineaccording to claim 1, further comprising cooling ducts, which lie behindor adjacent the stator windings when viewed from the magnets areassociated with said stator windings, wherein a temperature of thecooling ducts is controlled by means of a cooling medium.
 7. Injectionmolding machine according to claim 1, wherein the electric driving unitis also adapted to move a movable mould carrier towards a stationarymould carrier and away from stationary carrier and further adapted toapply a closing force.
 8. Injection molding mechanic according to claim7, and wherein there is a space in an interior of the third cylinder toaccommodate an ejector unit.
 9. Injection molding machine according toclaim 1, wherein the electric driving unit is also adapted to apply aclosing force.
 10. Injection molding machine according to claim 1,wherein the electric driving unit is also adapted to operate a drivingunit for fitting a nozzle onto an injection mould.
 11. Injection moldingmachine according to claim 1, wherein the electric driving unit is alsoadapted to move a feeding means in the injection moulding unit. 12.Injection molding machine according to claim 1, wherein the electricdriving unit is also adapted to operate an ejector unit.
 13. Injectionmolding machine according to claim 1, wherein the electric driving unitis also adapted to operate a core pulling unit on an injection mould.14. Injection molding machine according to claim 1, wherein the electricdriving unit is also adapted to operate a driving unit for a closurenozzle.